Okay... I've watched the translated Japanese cutscene. (Only the animated scenes)
There are minor difference between it and the English script. Very minor. Which means, if only judging by the animated cutscenes, the Japanese storyline isn't any better. There are still lots of unexplained things.
I just hope they'll add some new DLCs that include a bit of new story. After all, Super Sonic still isn't officially out yet. Hope is still there.